1. Field of the Invention
The present invention relates generally to the field of poly(1,3,4-oxadiazoles) and more particularly to poly(1,3,4-oxadiazoles) created via aromatic nucleophilic displacement reaction of di(hydroxyphenyl)-1,3,4-oxadiazoles with activated aromatic dihalides and activated aromatic dinitro compounds.
2. Description of the Prior Art
Poly(1,3,4-oxadiazoles) (POX) are heterocyclic polymers which were first synthesized by the reaction of bistetrazoles and diacid chlorides. [C. J. Abshire and C. S. Marvel, Makromolecular Chemistry, 44/46, 388 (1961)]. Since then several different reaction pathways have been developed to prepare these polymers. The most popular synthesis involves the preparation of a precursor polyhydrazide by the reaction of a diacid chloride or derivative with hydrazine or a dihydrazine compound. This precursor polyhydrazide is cyclized to the POX by heating to 200.degree.-300.degree. C. under vacuum or heating in a high boiling dehydrating solvent such as sulfuric or polyphosphoric acid. [A. H. Frazer and F. T. Wallenberger, Journal of Polymer Science, A-2, 1137, 1147, 1157 (1964)]. A different synthetic procedure produces POX in one step by the solution polymerization of a dicarboxylic acid or the corresponding nitrile, amide, or ester with hydrazine or its salt in polyphosphoric or sulfuric acid. [Y. Iwakura, K. Uno and S. Hara, A3, 45 Journal of Polymer Science (1965)]. Another method involves the self-polymerizing reaction of a dihydrazide in polyphosphoric or sulfuric acid. [Y. Iwakura, K. Uno and S. Hara, Makromol. Chem., 94, 103 (1966)]. The final preparation of POX is accomplished through the cyclodeammonation reaction of poly(N-acylhydrazidines), also referred to as poly(N-acylamidrazones), by heating in strong acids such as refluxing trifluoroacetic acid or polyphosphoric acid at 200.degree. C. [P. M. Hergenrother, Macromolecules, 3(1), 10 (1970); see also M. Saga and T. Shono, Journal of Polymer Science, B-4, 869 ( 1966)]. For a general review of poly(1,3,4-oxadiazoles) see "Thermally Stable Polymers" by P. E. Cassidy, Marcel Dekker, Inc. New York, p. 179; see also P. E. Cassidy and N. C. Fawcett, Journal of Macromolecular Science Reviews, C17(2), 209 (1979).